I don't think they click ads, I see friends checking out ads all the time. Particularly music ads. I'd imagine that it's not just a small-time thing, considering they're in the green now, but perhaps that money's coming from something else.
Their ads are also a lot better than they were a year ago. They target more effectively, within reason. (My ads are screwy since I list no information about myself, but they used to try and sell me Arrested Development t-shirts and they almost succeeded on multiple occasions.)
As I've said before, my money is on Facebook. People my age use it like it's the Internet. To them, that's all there is. And they click its ads.